The present invention relates to a measuring endoscope which enables one to measure the size of a morbid growth or the like within the body.
As a typical conventional apparatus for measuring the size of a morbid growth or the like within the body by means of an endoscope, there is known an apparatus, for example, which makes use of a device as shown in FIG. 1 through FIG. 4 (Gastroenterological Endoscopy, Vol. (25) 6, June, 1983, P. 868).
In FIG. 1, the endoscope apparatus has a laser light source 11 and a transmission type fiber diffraction grating 12; transmission type fiber diffraction grating 12 constituted by combining two sheets of a planar array of glass fibers so that the fiber bundles on one plane cross perpendicularly to those on the other plane. Since about 100 or more glass fibers each with, for example, a diameter of 25 .mu.m are arrayed close to each other to form a square, the transmission type fiber diffraction grating 12 has sides with dimensions of about 2.5 mm, which is quite adequate for mounting on the tip of a scope.
When laser beams from the laser light source 11 are incident at right angles on the transmission type fiber diffraction grating 12, a pattern projection light 13 is obtained as a two-dimensional spot like diffracted light arranged in matrix form. Projection of this light on a plane parallel to the transmission type diffraction grating 12 produces a two-dimensional matrix-like spot light pattern.
FIG. 2 shows the projected image of a spot light pattern when pattern projection light 13 is projected on a tilted screen from down below and viewed from above, at a location a prescribed distance away from the transmission type fiber diffraction grating 12. From the figure, there can be observed a phenomenon in which the interval between the spots increases in proportion to the distance away from the transmission type fiber diffraction grating, and, also, this increases as one moves towards the upper portion of FIG. 2.
In the conventional technique, the apparatus is so arranged as to measure the distance from an observation point to an object to be observed where a morbid growth or the like exists, as well as to measure the size and the degree of swelling or depression of the object.
FIG. 3 illustrates the situation where it becomes possible to measure the size of a morbid growth in an object to be measured 14 by generating changes in the interval between the spot lights projected on the object to be measured 14 in response to the form of the object to be measured 14, while giving a predetermined separation between the point of installation G of the transmission type fiber diffraction grating and a point of observation A, which is the point of installation of an object lens, image receiving element, or the like.
Now, in a measuring endoscope as in the above, there is generally arranged a source of white light which emits illumination light for observation, to provide a function for carrying out ordinary observation in addition to measurement.
However, if an illumination light for observation is incident on a living body or the like which is an object to be measured, simultaneous with the pattern projection light, halation is generated due to reflected light, as shown in FIG. 4. This leads to problems which make precise measurements difficult, such as the misrecognition of spots produced by the pattern projection light and the difficulty in the detection of spots because of the high background light levels resulting from background light due to the illumination for observation.
In addition, in the first example of the prior art described above, the glass fibers 12a and 12b with equal diameter, and hence producing an identical diffraction angle, are employed for the two sheets of one-dimensional fiber diffraction gratings, which together constitute a two-dimensional transmission type fiber diffraction grating 12, as shown in FIG. 5. This results in disadvantages in that detailed observation is difficult to make due to the observation points being distributed discretely as shown in FIG. 3, and that information on the unevenness of the object is visually more difficult to recognize.
FIG. 6 and FIG. 7 illustrate a second example of the prior art which compensates for the difficulties mentioned above.
In the second example of the prior art, it is attempted to recognize the unevenness by projecting a pinstripe pattern as shown in FIG. 7 on an object to be inspected, using a projection grating or reflection grating as shown in FIG. 6.
However, in the second example of the prior art, use is made only of light which either transmits through, or is reflected from, a part of the diffraction grating, so that the pinstripe pattern darkens due to reduction in the quantity of the pattern projection light, making it difficult to visualize the image.
To summarize, in the first example of the prior art, diffraction angles of the two sheets of one-dimensional fiber diffraction gratings, which together form a two-dimensional transmission type fiber diffraction grating, become identical so that detailed continuous measurement is difficult to realize due to discreteness of the points where measurement is to be made, leading to a problem in that unevenness information is visually more difficult to recognize.
On the other hand, in the second example of the prior art which was proposed to compensate for the difficulty in the first example, use is made only of light transmitted through or reflected from a portion of the grating, so the pinstripe pattern becomes dark due to a reduction in the quantity of the pattern projection light, resulting that the image is not easy to recognize.